"You will be the first to know: ain't gonna do it," he said during an interview on Vermont's WCAX-TV.

Speculation mounted that Sanders could run against Obama — it's unclear on what party label — after he spent over eight hours this month railing against the president's tax-cut deal on the Senate floor in a speech that came to be known as the "filibernie."

A website by the name of bernieforpresident.com, billing itself as "An independent and Quixotic plea for sanity," even turned up.

"Let’s face it, this will never happen," the site says. "But hey, why not at least put it out there."

Sanders says he is "very proud to be Vermont's senator."

"I am very content to be where I am, but I am flattered by that kind of response," he said.

If Sanders had decided to challenge Obama, he would have faced a steep climb. A recent Magellan Strategies poll found Obama with a 71-point lead over Sanders among registered voters in New Hampshire, a key early primary state.